CODEWITHSUNDEEP
dartflutter
bunny
bunny

Reputation: 1366

Flutter: How do i stop rendering "Widget build()" unnecessarily again and again?

This is a small POC in Flutter, where my build() function is being called again and again.

This was not expected at all without any loops and after a lot of research, I am calling "Future" in initState() as well.

But still facing the same issue.

Thank you in advance for time!

What have I tried..

import 'package:flutter/material.dart';

//http_request
import 'package:http/http.dart' as http; //to handle the http request
// import 'dart:async'; // for async functions
import 'dart:async' show Future;
import 'dart:convert'; //to convert the http response in JSON formate

import 'HomePage.dart';

    class Reports extends StatefulWidget {
      @override
      _Reports createState() => _Reports();
    }

    class _Reports extends State<Reports> {
  static String url = "Some Url";
  String _response = "abc";
  @override
  void initState() {
    super.initState();
    getTradeName_dropdown_ITR_Computation_DATA();
  }

  @override
  Widget build(BuildContext context) {

    print('body');

    return Scaffold(
      body: Container(
        child: new Text(_response),
      ),
    );
  }

  Future getTradeName_dropdown_ITR_Computation_DATA() async {
    try {
      http.Response response =
              await http.get("http://" + url );
      if (this.mounted) {
        setState(() {

          String jsonTradeName_dropdown = response.body;
          _response = jsonTradeName_dropdown;
        });
      }
    } on Exception {
      setState(() {
        _response = "Some error occored. Please Try again...";
      });
    }
  }
}

output:

I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body
I/flutter ( 5760): body

Upvotes: 3

Views: 3300

Answers (2)

Randal Schwartz
Randal Schwartz

Reputation: 44066

The proper model for understanding build() is that you should imagine it is being called sixty times a second. So your build() routine should be fast and idempotent.

In practice, there are optimizations made by the framework so that it isn't called except when needed, but you shouldn't view excessive calls to build() as a failure.

Upvotes: 1

CopsOnRoad
CopsOnRoad

Reputation: 267584

You were making couple of mistakes, here is the correct code. You should use a String instead of a Text widget to show the response. 

class _Reports extends State<Reports> {
  static String url = "url";
  String _response = "abc";
  @override
  void initState() {
    super.initState();
    getTradeName_dropdown_ITR_Computation_DATA();
  }

  @override
  Widget build(BuildContext context) {

    print('body');

    return Scaffold(
      body: Container(
        child: new Text(_response),
      ),
    );
  }

  Future getTradeName_dropdown_ITR_Computation_DATA() async {
    try {
      http.Response response =
      await http.get("url_goes_here");

      if (this.mounted) {
        setState(() {
          String jsonTradeName_dropdown = response.body;
          _response = jsonTradeName_dropdown;
        });
      }
    } on Exception {
      setState(() {
        _response = "Some error occored. Please Try again...";
      });
    }
  }
}

Upvotes: 1

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